1. Field of the Invention
The present invention relates to power saving procedures conducted in a communication network. In particular, the present invention relates to a method, apparatus and computer program product providing a mechanism for power saving procedures to be conducted in transmission network nodes, such as base stations or the like, in a heterogeneous network environment.
2. Related background Art
Prior art which is related to this technical field can e.g. be found by the technical specifications TS 32.762 (current version: 9.3.1), TS 23.401 (current version: 9.4.0), TS 36.423 (current version: 9.2.0) and technical report TR 32.826 (current version: a.0.0) etc. of the 3GPP.
The following meanings for the abbreviations used in this specification apply:    3GPP—3rd generation partnership project    DL—downlink    eNB—enhanced node B (base station)    ES—energy saving    EUTRAN—enhanced UTRAN    FDD—frequency division duplexing    IOC—information object class    IoT—interference over thermal    IP—Internet protocol    LTE—long term evolution    OAM—operation, administration and maintenance (or management)    RACH—random access channel    RAN—radio access network    RX—reception    SOON—self-organized and optimized network    TX—transmission    UE—user equipment    UL—uplink    UTRAN—universal terrestrial RAN
In the last years, an increasing extension of communication networks, e.g. of wire based communication networks, such as the Integrated Services Digital Network (ISDN), DSL, or wireless communication networks, such as the cdma2000 (code division multiple access) system, cellular 3rd generation (3G) communication networks like the Universal Mobile Telecommunications System (UMTS), enhanced communication networks based e.g. on LTE, cellular 2nd generation (2G) communication networks like the Global System for Mobile communications (GSM), the General Packet Radio System (GPRS), the Enhanced Data Rates for Global Evolutions (EDGE), or other wireless communication system, such as the Wireless Local Area Network (WLAN) or Worldwide Interoperability for Microwave Access (WiMAX), took place all over the world. Various organizations, such as the 3rd Generation Partnership Project (3GPP), Telecoms & Internet converged Services & Protocols for Advanced Networks (TISPAN), the International Telecommunication Union (ITU), 3rd Generation Partnership Project 2 (3GPP2), Internet Engineering Task Force (IETF), the IEEE (Institute of Electrical and Electronics Engineers), the WiMAX Forum and the like are working on standards for telecommunication network and access environments.
Generally, for properly establishing and handling a communication connection between network elements such as a UE and another communication equipment, such as a database, a server, etc., one or more intermediate network elements, such as network control nodes, support nodes, service nodes and interworking elements are involved which may belong to different communication networks.
Low power consumption is an important performance indicator for communication network operators and the users of a cellular phone. At present, power consumption of a UE is typically described in terms of battery life time, and more specifically in terms of talk time and standby time. On the network side the power consumption is described as the power consumption of network elements, such as transmission nodes or access nodes, wherein power consumption is measured for different configuration and load situations.
In principle the access node power consumption for zero load over the air interface could be seen then as the standby time of an access node. It is to be expected that those measures are playing more and more important role in the node design and network configuration.
On the other hand, with regard to the UE, for the terminal standby time, it is necessary to take into account the fact that usually in wireless communication networks even if a user is not doing any call the mobile phone is consuming power. For example, when being switched on but not making any call, which is also referred to that a UE is in an idle mode, the UE usually searches periodically for its environment, e.g. synchronization sequences, reference signals and downlink broadcast channels or the like (the elements to be searched for are defined in the different communication network standards and may be different depending on the actual type of network). Furthermore, when the UE is in the idle mode, downlink pilot signals may be received, and usually it is required to permanently run circuitry by means of which paging channel information can be detected in order to get activated if a call is received.
However, a problem of such procedures conducted in the UE is that the actual power consumption caused by such a processing can be hardly foreseen and may increase remarkably in some cases. For example, in the context of so-called heterogeneous networks, power consumption in UEs caused by such a processing may be extreme. In a heterogeneous network structure, access nodes like base stations, relay nodes and low power access nodes (e.g. pico and femto access nodes) are deployed in a co-channel mode with a plurality of overlapping cell areas so as to provide a more regular user performance in connected mode and to satisfy increasing capacity needs. For such an environment, the usual environment monitoring and power saving strategies implemented in UEs are not optimal as they are not fine-tuned for those deployments. Especially the idle mode power consumption of a UE may be increased due to the increased number of access nodes per square area.
Therefore, one approach to keep power consumption at a reasonable level is to keep the number of active access nodes as low as possible, for example during network capacity off peak hours.
In detail, to keep the UE stand by time at reasonable level, complex and power consuming computations in the UE should be performed as infrequently as possible wherein it has to be ensured that the user experience (e.g. in terms of cell selection and paging delay) is not deteriorated. For example, in idle mode, corresponding operations concern operations on the synchronization sequences, reference and paging signals as well as the decoding of the DL broadcast channel.
With heterogeneous network co-channel deployments the problem however is that the number of received and decode-able signals from surrounding transmission nodes is significantly higher compared with the non-heterogeneous case. Therefore, UE procedures like cell selection or cell reselection are triggered more frequently. Main reason for this is the high density of transmission nodes per square area which are deployed to provide the more regular user performance in connected mode and to satisfy the increasing capacity needs.
Therefore, in order to deal with this issue of increased UE battery consumption and to reduce the network power consumption in heterogeneous networks without harming the system performance, it has been proposed to switch off the capacity increasing transmission nodes, such as relay nodes and low power transmission nodes (hotspots, pico and femto nodes) when it is suitable, e.g. during off peak network times with low traffic load. For this purpose, the following solutions are proposed which are specified for a heterogeneous co-channel case:                Transmission node (such as an eNB or the like) switch off: autonomous switch off decision can be done by individual nodes e.g. based on load thresholds. Before a node is switched off the neighbor nodes are informed after the decision is made.        Transmission node (eNB) switch on: switch on should be performed upon request by one neighbor transmission node or is done by individual decision of switched off node. In case of switch on by neighbor request, the requesting node is informed about outcome of the request, and all other neighbors are informed in case of switch on.        